Although arsenic is a known human carcinogen and induces cancers of the skin, lung, liver and bladder, the underlying carcinogenic mechanism(s) is not known. The US Environmental Protection Agency has placed arsenic at the top of its superfund contamination list. One of the main difficulties in studying mechanisms of arsenic carcinogenesis is the lack of a suitable human cell model whereby the various tumorigenic stages can be dissected and the molecular changes associated with each stage examined. While preliminary data obtained by the applicant has shown that arsenic can induce malignant transformation of papillomavirus-immortalized human bronchial epithelial (BEP2D) cells, this model is not ideal due to the presence of viral oncoproteins. The newly established telomerase (hTERT) -immortalized human bronchial epithelial (IMNHBE) cell transformation model that has normal p53 and p16 functions represents an attractive alternative to further ascertain the mechanism involved in arsenic-induced bronchial carcinogenesis. A series of cellular and molecular assays will be conducted using isolated clonal cell lines at each stage of the carcinogenic process to identify the necessary changes essential for arsenic carcinogenesis. The proposal has 2 main objectives: The first is to establish an in vitro human epithelial cell transformation model for arsenic carcinogenesis using two independent, telomerase-immortalized bronchial epithelial cell lines; and the second goal is to examine the mechanism(s) involved, particularly loss of tumor suppressor functions, associated with each stage of the carcinogenic process. A series of 7 specific aims are proposed to address 4 testable hypotheses. The IM NHBE cells are anchorage dependent and do not form tumors in immunosuppressed host animals. CDNA arrays coupled with functional analysis at the gene level will be conducted using tumors and cells from intermediate transformation stages to provide a mechanistic basis for arsenic-induced bronchial carcinogenesis.